Semiconductor device having inter-metal dielectric patterns and method for fabricating the same

ABSTRACT

A method for fabricating semiconductor device includes the steps of first forming a first inter-metal dielectric (IMD) layer on a substrate, patterning the first IMD layer to form first IMD patterns on the substrate, a trench surrounding the first IMD patterns, and a second IMD pattern surrounding the trench, forming a metal layer in the trench to surround the first IMD patterns, forming a second IMD layer on the first IMD patterns, the metal layer, and the second IMD pattern, and forming via conductors in the second IMD layer. Preferably, the via conductors not overlapping the first IMD patterns.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device,and more particularly to a method of using patterning process to forminter-metal dielectric (IMD) patterns and patterned metal layer.

2. Description of the Prior Art

As device dimensions continue to shrink, a reduction in interconnectline widths leads to increased line resistance (R) for signals. Further,reduced spacing between conducting lines creates more parasiticcapacitance (C). The result is an increase in RC signal delay, whichslows chip speed and lowers chip performance.

The line capacitance, C, is directly proportional to the dielectricconstant, or k-value of a dielectric material. A low-k dielectricreduces the total interconnect capacitance of the chip, reduces the RCsignal delay, and improves chip performance. Lowering the totalcapacitance also decreases power consumption. The use of a low-kdielectric material in conjunction with a low-resistance metal lineprovides an interconnect system with optimum performance for the ULSItechnology. For this reason, prior art attempts to reduce the RC delayshave focused on utilizing material with a low-k to fill the gaps betweenthe metal lines.

Nevertheless, a difference in stress often arises between lower levelmetal interconnections and IMD layers made of low-k dielectric materialduring fabrication of semiconductor devices. Typically, tensile stressis more likely to be generated between lower level metalinterconnections while compressive stress is likely to be generated forIMD layers. This unbalance between different stresses ultimately createscracks particularly in dense regions of via conductors and affects theperformance of the device significantly. Hence how to resolve this issuehas become an important task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating semiconductor device includes the steps of first forming afirst inter-metal dielectric (IMD) layer on a substrate, patterning thefirst IMD layer to form first IMD patterns on the substrate, a trenchsurrounding the first IMD patterns, and a second IMD pattern surroundingthe trench, forming a metal layer in the trench to surround the firstIMD patterns, forming a second IMD layer on the first IMD patterns, themetal layer, and the second IMD pattern, and forming via conductors inthe second IMD layer. Preferably, the via conductors not overlapping thefirst IMD patterns.

According to another aspect of the present invention, a semiconductordevice includes a patterned metal layer on a substrate, via conductorson the patterned metal layer, and first inter-metal dielectric (IMD)patterns embedded in the patterned metal layer. Preferably, the firstIMD patterns are between and without overlapping the via conductors in atop view.

According to yet another aspect of the present invention, asemiconductor device includes a patterned metal layer on a substrate,first inter-metal dielectric (IMD) patterns embedded in the patternedmetal layer, and via conductors on the patterned metal layer.Preferably, the via conductors not overlapping the first IMD patterns.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 illustrate a method for fabricating semiconductor deviceaccording to an embodiment of the present invention.

FIG. 6 illustrates a structural view of a semiconductor device accordingto an embodiment of the present invention.

FIG. 7 illustrates a structural view of a semiconductor device accordingto an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, in which left portion of FIG. 1 illustrates a topview for fabricating a semiconductor device according to an embodimentof the present invention and right portion of FIG. 1 illustrates across-section view of the left portion of FIG. 1 taken along thesectional line AA′. As shown in FIG. 1, a substrate 12, such as asubstrate composed of semiconductor material is provided, in which thesemiconductor material could be selected from the group consisting ofsilicon, germanium, silicon germanium compounds, silicon carbide, andgallium arsenide. Active devices such as metal-oxide semiconductor (MOS)transistors, passive devices, conductive layers, and interlayerdielectric (ILD) layer (not shown) could also be formed on top of thesubstrate 12. More specifically, planar MOS transistors or non-planar(such as FinFETs) MOS transistors could be formed on the substrate 12,in which the MOS transistors could include transistor elements such asmetal gates, source/drain regions, spacers, epitaxial layers, andcontact etch stop layers (CESL). Preferably, the ILD layer could beformed on the substrate 12 and covering the MOS transistors and contactplugs could be formed in the ILD layer to electrically connect to thegate and/or source/drain region of MOS transistors. Since thefabrication of planar or non-planar transistors and ILD layer is wellknown to those skilled in the art, the details of which are notexplained herein for the sake of brevity.

Next, an IMD layer 14 is formed on the ILD layer, in which the IMD layer14 could include but not limited to for example nitrogen doped carbide(NDC) or silicon carbon nitride (SiCN). It should be noted that sincethe IMD layer 14 has not been patterned at this stage, the IMD layer 14is disposed entirely on the surface of the lower level IMD layer and/orsubstrate 12 if viewed from a top view perspective.

Referring to FIG. 2, in which left portion of FIG. 2 illustrates amethod for fabricating semiconductor device following FIG. 1 accordingto an embodiment of the present invention and right portion of FIG. 2illustrates a cross-section view of the left portion of FIG. 2 takenalong the sectional line AA′. As shown in FIG. 2, a pattern transferprocess is conducted to pattern the IMD layer 14 for forming a pluralityof first IMD patterns 16, a trench 18, and a second IMD pattern 20.Specifically, the step for patterning the IMD layer 14 conducted at thisstage could be accomplished by first forming a patterned mask (notshown) such as a patterned resist on the IMD layer 14, and then usingthe patterned mask as mask to remove part of the IMD layer 14 throughetching process for patterning the IMD layer 14 into a plurality offirst IMD patterns 16 on the substrate 12 or ILD layer, a trench 18surrounding the first IMD patterns 16, and a second IMD pattern 20surrounding the trench 18. If viewed from a top view perspectiveaccording to the left portion of FIG. 2, each of the first IMD patterns16 formed at this stage preferably share equal size, each of the firstIMD patterns 16 preferably include a quadrilateral such as a rectangleor square while the first IMD patterns 16 are even distributed orscattered within the trench 18 or arranged according to an array.

Referring to FIG. 3, in which left portion of FIG. 3 illustrates amethod for fabricating semiconductor device following FIG. 2 accordingto an embodiment of the present invention and right portion of FIG. 3illustrates a cross-section view of the left portion of FIG. 3 takenalong the sectional line AA′. As shown in FIG. 3, a metal layer 22 isformed to fill the trench 18 entirely, in which the metal layer 22 whilehaving the shape of the trench 18 could also be referred to as apatterned metal layer 22 that surrounds all of the first IMD patterns16. Preferably, the entire patterned metal layer 22 surrounding thefirst IMD patterns 16 at this stage is at same electrical potential. Inthis embodiment, the metal layer 22 preferably includes copper (Cu), butcould also include other materials including but not limited to forexample tungsten (W), aluminum (Al), titanium aluminide (TiAl), cobalttungsten phosphide, CoWP), or combination thereof.

Referring to FIGS. 4-6, in which FIG. 4 illustrates a method forfabricating semiconductor device following FIG. 3 according to anembodiment of the present invention, the left portion of FIG. 5illustrates a cross-section view of FIG. 4 taken along the sectionalline AA′, the right portion of FIG. 5 illustrates a cross-section viewof FIG. 4 taken along the sectional line BB′, and FIG. 6 illustrates atop view for fabricating semiconductor device according to an embodimentof the present invention. As shown in FIGS. 4-5, a stop layer 24 and anIMD layer 26 are formed to cover the metal layer 22, the first IMDpatterns 16, and the second IMD pattern 20, and one or morephoto-etching process is conducted through a single damascene or dualdamascene process to remove part of the IMD layer 26 and part of thestop layer 24 for forming a plurality of contact holes (not shown)exposing the metal layer 22 underneath, in which the contact holespreferably not overlapping any of the first IMD patterns 16 and secondIMD pattern 20.

Next, conductive materials or metals including a barrier layer selectedfrom the group consisting of titanium (Ti), titanium nitride (TiN),tantalum (Ta), and tantalum nitride (TaN) and a low resistance metallayer selected from the group consisting of W, Cu, Al, TiAl, and CoWPare deposited into the contact holes. Next, a planarizing process suchas chemical mechanical polishing (CMP) is conducted to remove part ofthe barrier layer and low resistance metal layer for forming contactplugs or metal interconnections 32 made of via conductors 28 and trenchconductors 30 electrically connecting the lower level metal layer 22.Since single damascene and dual damascene process are well known tothose skilled in the art, the details of which are not explained hereinfor the sake of brevity. In this embodiment, the metal interconnections32 preferably includes copper, the stop layer 24 preferably includessilicon nitride (SiN), and the IMD layer 26, first IMD patterns 16, andsecond IMD pattern 20 preferably include dielectric materials includingbut not limited to for example silicon oxide (SiO₂), tetraethylorthosilicate (TEOS), nitrogen doped carbide (NDC), or silicon carbonnitride (SiCN).

It should be noted that to emphasize the arrangement of the viaconductors 28 and lower level metal layer 22, only the via conductors 28are shown in the top view in FIG. 4 while the trench conductors 30 areomitted for clarity purpose. Moreover, in addition to using theaforementioned patterning approach to form the first level patternedmetal layer 22 within the patterned first IMD patterns 16 and second IMDpattern 20, it would also be desirable to apply the patterning approachfor patterning the first level metal layer 22 to second level metalinterconnections such as the trench conductors 30 or even higher levelmetal interconnections. Preferably, patterns formed by the second levelmetal interconnections through the aforementioned patterning processincluding metal layer patterns and/or IMD patterns could be having samepatterns or different patterns as the first level metalinterconnections, which are all within the scope of the presentinvention.

Referring again to FIGS. 4-6, FIGS. 4-6 further illustrate a structuralview of a semiconductor device according to an embodiment of the presentinvention. As shown in FIGS. 4-6, the semiconductor device includes apatterned metal layer 22 disposed on the substrate 12, a plurality ofvia conductors 28 disposed on the patterned metal layer 22, a pluralityof first IMD patterns 16 embedded in the patterned metal layer 22, and asecond IMD pattern 20 surrounding the patterned metal layer 22.

In this embodiment, the via conductors 28 are arranged on the patternedmetal layer 22 along a first direction (such as X-direction) in a topview and the first IMD patterns 16 are arranged between the viaconductors 28 along the same first direction while not overlapping thevia conductors 28, in which the first IMD patterns 16 are evenlydistributed on the patterned metal layer 22 instead of clustering aroundthe via conductors 28. Since the patterned metal layer 22 and the andthe first IMD patterns 16 are disposed on the same level, the topsurfaces of the patterned metal layer 22 and the first IMD patterns 16are preferably coplanar according to a cross-section view. According toan embodiment of the present invention, if the first IMD patterns 16 onthe first level are arranged along a first direction such as theX-direction, the IMD patterns on the second level could have either sameor different arrangement as the first IMD patterns 16 on the firstlevel. For instance, the IMD patterns on the second level could bearranged along the same X-direction as the first IMD patterns 16 orcould be arranged along Y-direction, which are all within the scope ofthe present invention.

If viewed from a top view perspective, the patterned metal layer 22preferably includes a quadrilateral, each of the via conductors 28includes a square, and each of the first IMD patterns 16 includes asquare, in which the area of each of the first IMD patterns 16 isslightly greater than the area of each of the via conductors 28.Nevertheless, according to other embodiments of the present invention,it would also be desirable to adjust the size of the first IMD patterns16 so that the area of each of the first IMD patterns 16 could be equalto or less than the area of each of the via conductors 28, which are allwithin the scope of the present invention.

Moreover, as shown in FIG. 6, in contrast to the aforementionedembodiment of forming square first IMD patterns 16 while patterning theIMD layer 14 in FIG. 2, it would also be desirable to adjust the size orshape of the mask to form substantially rectangular first IMD patterns16 in the trench. Next, processes from FIGS. 3-5 are conducted to formelements such as the patterned metal layer 22, stop layer 24, IMD layer26, and metal interconnections 32, which is also within the scope of thepresent invention.

Referring to FIG. 7, FIG. 7 illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 7, in contrast to both the first IMDpatterns 16 and via conductors 28 having square-shaped top view as shownin FIG. 4, it would also be desirable to adjust the pattern of mask usedduring formation of the aforementioned elements or carry out correctingstep through optical proximity correction (OPC) process so that theshape of each of the first IMD patterns 16 and via conductors 28 couldinclude a circle or substantially circular shape if viewed from a topview perspective, which is also within the scope of the presentinvention.

Overall, the present invention first forms a first IMD layer on thesubstrate and then pattern the first IMD layer to form a plurality offirst IMD patterns, a trench surrounding the first IMD patterns, and asecond IMD pattern around the trench. Next, a metal layer is depositedinto the trench, a second IMD layer is formed, and a plurality of viaconductors are formed in the second IMD layer to electrically connectthe metal layer underneath. By using the above approach to embed IMDpatterns evenly arranged according to an array within the metal layer,it would be desirable to balance or relieve the stress between lowerlevel and higher level metal interconnect structures without onlyreducing stress locally or concentrated around a single via conductor.Ideally, it would be desirable to improve the issue of cracks generatednot only in dense region but also in all other areas of metalinterconnect structure as a result of uneven stress.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for fabricating semiconductor device,comprising: forming a first inter-metal dielectric (IMD) layer on asubstrate; patterning the first IMD layer to form first IMD patterns onthe substrate, a trench surrounding the first IMD patterns, and a secondIMD pattern surrounding the trench; forming a metal layer in the trenchto surround the first IMD patterns; forming a second IMD layer on thefirst IMD patterns, the metal layer, and the second IMD pattern; andforming via conductors in the second IMD layer, wherein the viaconductors not overlapping the first IMD patterns.
 2. The method ofclaim 1, wherein top surfaces of the metal layer and the first IMDpatterns are coplanar.
 3. The method of claim 1, wherein the metal layercomprises copper, aluminum, tungsten, titanium aluminide, or cobalttungsten phosphide.
 4. The method of claim 1, wherein the via conductorsare arranged on the metal layer along a first direction in a top view.5. The method of claim 4, wherein the first IMD patterns are arrangedbetween the via conductors along the first direction in a top view. 6.The method of claim 1, wherein a shape of the metal layer comprises aquadrilateral in a top view.
 7. The method of claim 1, wherein a shapeof each of the via conductors comprises a square or a circle in a topview.
 8. The method of claim 1, wherein a shape of each of the first IMDpatterns comprises a square or a circle in a top view.
 9. The method ofclaim 1, wherein a shape of each of the first IMD patterns comprises arectangle in a top view.